xml: added escape, unescape, validate subcommands

pages/common/xml-validate.md

@@ -1,7 +1,23 @@
 # xml-validate
 
 > XMLStarlet toolkit: Validate XML documents.
-> More information: <https://http://xmlstar.sourceforge.net/doc/xmlstarlet.pdf>.
+> More information: <http://xmlstar.sourceforge.net/doc/xmlstarlet.pdf>.
+
+- Validate XML document for well-formedness only (default):
+
+`xml validate --well-formed {{path/to/input1.xml|URI}} {{input2.xml ...}}`
+
+- Validate XML document against Document Type Definition (DTD):
+
+`xml validate --dtd {{path/to/schema.dtd}} {{path/to/input1.xml|URI}} {{input2.xml ...}}`
+
+- Validate XML document against XML Schema Definition (XSD):
+
+`xml validate --xsd {{path/to/schema.xsd}} {{path/to/input1.xml|URI}} {{input2.xml ...}}`
+
+- Validate XML document against a Relax NG schema (RNG):
+
+`xml validate --relaxng {{path/to/schema.rng}} {{path/to/input1.xml|URI}} {{input2.xml ...}}`
 
 - Display help for `validate` subcommand: